The present invention relates to a light polarizing spectacle lens and to a process for making the light polarizing spectacle lens.
The successful manufacture of a high quality light polarizing spectacle lens is hampered by several problems that have resisted solution. The problems are associated with an outer lens resin and an inner polarizing film combining with the outer lens resin to make the light polarizing lens product.
One problem encountered in manufacturing a light polarizing lens is the problem of undesired cylindrical power in a finished lens. The problem of undesired cylindrical power arises when front curvatures of a semi-finished lens vary excessively when measured in a horizontal and a vertical meridian. For some lenses, curvatures vary by more than 0.12 diopters. The Laliberte U.S. Pat. No. 3,674,587, issued on Jul. 4, 1972, describes a method for positioning a sheet of polarizing film in a cast polymer in an attempt to reduce though not eliminate an undesired cylindrical power. The Laliberte patent describes the polarizing film as being in close proximity to the front of one cast optical element, but remaining completely embedded within a casting.
Another related problem of manufacturing polarizing lenses concerns making a thick rather than a thin lens. Light polarizing lenses typically have an undesirable thickness within both the center of the lens and at the edge of the lens.
A third problem encountered in making a polarizing spectacle lens is the problem of delamination. Delamination describes a separation of the layers of different materials used to make a polarizing spectacle lens. Light polarizing lenses have a particular problem of delaminating when dipped in a dye bath having a temperature near the boiling point of water for longer than fifteen minutes. The Arond et al. U.S. Pat. No. 3,208,902, issued on Sep. 28, 1965, describes the use of an adhesive to bond the layers of a polarizing lamination in order to reduce the delamination problem for lenses exposed to water immersion and dry heat.
The Ortlieb U.S. Pat. No. 3,786,119, issued on Jan. 15, 1974, describes a method of cutting the polarizing film into screens of appropriate form with suitable axial direction, curving the screens and covering the curved screens with an attachment varnish. The screens are then placed in molds. The molds are filled with a polymerizable or poly-condensible liquid resin.
A fourth problem encountered in the manufacture of light polarizing lenses includes the migration of lens polymer constituents such as plastisizers and catalysts into the light polarizing film. The migrating constituents can damage the polarizing film by causing the film to deform on a micro scale. The migrating material can also bleach dyes in the light polarizing film and film carrier. As a consequence, the color consistency from lens-to-lens is poor. The color inconsistency promotes waste by preventing the mounting of two lenses in the same spectacle frame. The Schuler patent, U.S. Pat. No. 3,940,304, issued Feb. 24, 1976, describes a step of coating the light polarizing film with a tiecoat-barrier to stop undesirable migration. The Schuler patent, U.S. Pat. No. 3,833,289, issued Sep. 3, 1974, describes the use of cross-linked nitrocellulose and one other polymer to act as a barrier between the light polarizing film and lens polymer. Attempts to reduce migration have resulted in weak adhesion between a lens body and a film carrier.
A fifth problem in the manufacture of polarizing spectacle lenses is a hazing of the light polarizing lens. Hazing is a defect introduced by the propagation of micro-cracks during manufacture of the lens. The hazing problem occurs when the polarizing film is combined with an outer lens polymer, typically in a lens mold. One cause of hazing includes an uneven polymerization of the outer lens polymer. The Weinberg U.S. Pat. No. 3,171,869, issued on Mar. 2, 1965, describes a process for casting the outside lens polymer at a temperature within an approximate range of 257.degree. F. and 455.degree. F. in order to control uneven polymerization and to reduce hazing. Specifically, with the Weinberg process, the lens is temporarily softened by heat so that the polymer chains have sufficient mobility to be bonded together in cross-links. Upon cooling the lens, the softness disappears due to the restoration of attractive forces, partially responsible for the hardness which is displayed by the lens at room temperature.
Hazing has also been initiated by accidental concentration of the lens polymer in a particular region of the lens. The accidental concentration creates a stress center from which fracture may begin. The Weinberg patent describes the use of a polymerization catalyst to reduce the accidental concentration hazard.
A second cause of hazing results from the attractive forces responsible for lens hardness. The attractive forces include covalent bonds formed in a gel stage of the polymerization of the lens polymer. While covalent bonds have the desirable features of hardening a lens and of imposing scratch resistance on the lens, covalent bonds have an undesirable feature of shrinking the lens as it cools. The shrinkage of the lens polymer sets up internal stresses that can cause hazing.
A third cause of hazing includes inducing a curve into a light polarizing film. A consequence of improperly inducing the curve includes introducing stresses and cracks into the film. The Ceppi U.S. Pat. No. 3,560,076, issued on Feb. 2, 1971, describes constructing the light polarizing film so that the light polarizing film is thicker on a convex side than on a concave side.
The Schuler U.S. Pat. No. 3,711,417, issued on Jan. 16, 1973, describes the use of a particular type of monomer to reduce the possibility of lens hazing. The monomer described has the following general formula: EQU CH.sub.3 --CH.sub.2 --(CH.sub.2 --CH.sub.2 --O).sub.x --CH.sub.2 --CH.sub.2 --O--CO--CR.dbd.CH.sub.2.